The present invention relates to modular conveying apparatus.
Because they do not corrode, are light weight, and are easy to clean, unlike metal conveyor belts, plastic conveyor belts are used widely, especially in conveying food products. Modular plastic conveyor belts are made up of molded plastic modular links, or belt modules, that can be arranged side by side in rows of selectable width. A series of spaced apart link ends extending from each side of the modules include aligned apertures to accommodate a pivot rod. The link ends along one end of a row of modules are interconnected with the link ends of an adjacent row. A pivot rod journaled in the aligned apertures of the side-by-side and end-to-end connected modules forms a hinge between adjacent rows. Rows of belt modules are then connected together to form an endless conveyor belt capable of articulating about a drive sprocket.
In some applications the belt modules are provided with a rib disposed across the mid-portion of the module. The cross-rib is disposed perpendicular to the direction of belt travel and provides a driving surface capable of engaging with the teeth of the drive sprocket. The shape of the sprocket tooth and engaging cross-rib are designed for the best performance and maximum torque transmission from the sprockets to the belt. Preferably the design avoids the disengagement of the sprocket due to the sprocket slipping radially out of engagement with the cross-rib. Referring to FIG. 1, in order to move the sprocket tooth smoothly into engagement without collision between the tooth corner and the face 7 of the rib 9, the angle 10 of the engaging rib face 7 (right side of FIG. 1) with respect to axis 13 in FIG. 1 has to be less than or equal to ninety degrees with ninety degrees being the preferred angle. Also, as the distance 16 increases, the angle of sprocket engagement becomes steeper and the risk of disengagement under high torque is reduced. For bi-directional drives, two sprocket teeth are used on both sides of the central rib. The teeth engage on the left face or on the right face of the rib 9 depending on the direction of belt travel. The optimization of the cross-rib 9 according to the above-described parameters leads to a very thick cross-rib as shown in FIG. 1.
What is needed is a module design that provides an optimal design with regard to torque transmission yet avoids the thick cross-rib 9 shown in FIG. 1.
The present invention meets the above-described need by providing a module having a cross-rib that is alternately offset from a centerline of the module and that is used in connection with a double row sprocket with alternating sprocket teeth.